1. Field of the Invention
This invention relates to radial tires for heavy load vehicles and more particularly to a giant radial tire for off-road vehicles which is obliged to be used under a heavy load and which is provided with a highly durable bead portion.
2. Description of the Prior Art
The bead portion of the above mentioned kind of tire has heretofore frequently induced a separation failure due to its poor durability. That is, the durability of the bead portion is dependent on the strain and heat produced due to deformation caused by the load subjected to the tire. This load deformation becomes larger as the load subjected to the radial tire becomes heavy in response to its use and becomes the maximum when the radial tire is used for off-road vehicles. In addition, the giant radial tire representing the radial tires for the above mentioned kind of use has the disadvantage that radiation of heat is poor owing to the remarkably large volume of the tire if compared with that of the tires used for the other purposes.
Influence of such strain and heat causes troubles with respect to the above mentioned durability of the bead portion where the above mentioned strain and heat are maximum.
Investigations on the cause of the separation failure induced in the bead portion of the above mentioned kind of tire have demonstrated the result that the crack produced at the end portion of the tire skeleton such as the ply cord end or chafer cord end reaches the surface of the tire so as to induce the separation failure of the bead portion, thereby finally making the tire unable to use.
Many attempts have heretofore been proposed to eliminate the above mentioned separation failure, for example, the end portion of the wire cord such as metal cord particularly steel cord is changed in position or the cord end is covered with organic textile cord fabric or rubber sheet having special property, or organic textile cord layer or considerably extensible wire cord layer is disposed near the cord end. These measures have been applied separately or in combination thereof, but none has led to satisfactory result.